Certain chemical processes involve the interaction of two liquids or fluids of different densities and limited mutual solubility. When these liquids are mixed to form a two-phase system and are then catalytically reacted under strongly exothermic or endothermic conditions, it becomes desirable and even necessary to achieve an intermixing between the two liquids before they are subjected to reaction conditions. With liquids of differing density, it is particularly difficult to achieve a distribution of one liquid in the other, or vice versa, on a uniform basis, even transitorily, because of the inherent physical tendency of such liquids to assume different flow rates, even with all other variables being substantially constant.
For example, the hydration of acrylonitrile to acrylamide is a highly exothermic reaction. The problem of controlling reaction temperature is particularly, and perhaps even uniquely, difficult when using a reactor feed of relatively high acrylonitrile concentration due to the relatively low system heat capacity per mole of reactant acrylonitrile. This results in the necessity of conducting the reaction between acrylonitrile and water when using a concentrated acrylonitrile feed in a reaction zone from which the heat of reaction can be continuously removed to avoid undesirably high temperatures where side reactions may occur.
As those skilled in the art will appreciate, if the heat of reaction is continuously removed from a fixed-bed catalytic reaction zone, the zone or zonal elements must have a relatively small cross-sectional area with a coolant circulated around the outside of the zone or zonal elements. If large cross sectional areas are used for the zone or zonal elements, some areas of the reaction zone are too far from the cooling surface and hence tend to experience undesirably large temperatures. In addition, a small cross sectional area tends to maximize the interfacial area between the reaction zone and the cooling media, which allows removing the heat of reaction efficiently with a relatively small temperature difference between reaction zone and cooling media. In common, normal practice using a tubular reaction zone with a fixed catalytic bed in the zones, it is common to employ tubes having inside diameters in the range of from about 0.4 to 2.6 inches with a circular cross section.
In the case of acrylamide production by a hydrolysis of acrylonitrile, one employs a reaction having a sufficiently large catalyst bed volume to produce commercial quantities of acrylamide at commercial rates. The particular reactor design used can be one which has a multiplicity of longitudinally parallel, transversely spaced tubes positioned within a common shell through which a coolant is circulatable. A single tube is not used because the bed length would be impractically long for a commercial reactor.
In such a reactor or reactors, the feed composition used in making a concentrated acrylamide solution directly is inherently two phased because of the limited solubility of acrylonitrile in water. In a commercial size reaction having a multiplicity of parallel tubes, it is critically important that all tubes receive approximately the same total flow rate per tube of each of the two phases. Thus, if a substantial deviation occurs from this desired equal distribution, the reactor conversion performance will be inherently reduced. In the extreme case, where essentially all water goes through one set of tubes, while substantially all acrylonitrile goes through another set of tubes, conversion is essentially zero.
The achievement of such a mixture having substantially uniform distribution of water and acrylonitrile in two phases at the entrance to each of a multiplicity of reactor tubes presents a formidable problem which does not appear to be solvable by any known technique.